Hydrogen cyanide (HCN) is one of the most simple interstellar molecules. Thanks to its large dipole moment (2.99 Debye; [1]}), its rotation transitions are good probe of dense molecular gas in Galactic and extragalactic environments.
HCN and its isomer hydrogen isocyanide HNC are thought to play an important role in the formation of more complex molecules, like cyanopolyynes HC\(_{2n+1}\) N, either in dark cloud cores [2]} or in more energetic regions, like protostellar shocks [3]}. Since HCN and HNC have similar energy spectra and dipole moments, their differences in spatial distribution is mainly related to the gas chemical conditions. For this reason, they have often been used as probes of gas chemical evolution in both dense cores and
star-forming regions [4]}, [5]}, [6]}.
